The mechanism of action of epidermal growth factor (EGF) on hepatocytes in primary culture will be investigated in conjunction with experiments to elucidate the role of this hormone in the control of insulin secretion by the pancreas. Since EGF and insulin have been shown to act synergistically on liver, it is important to investigate the factors controlling the release of these two hormones into the blood and how this might be linked to the regenerative process in liver. These studies are designed to provide deeper insight into the process of liver regeneration and into factors causing pancreatic insufficiency leading to the disorder, diabetes mellitus. A homogeneous population of adult rat liver parenchymal cells maintained as nondividing primary cultures will be used as a model system to investigate the mechanism of action and biological effects of EGF on the liver. We have already determined that 125I-labeled EGF is capable of binding to these cultured hepatocytes in a specific and saturable manner. Attempts will be made to determine if the membrane-bound 125I-EGF acts only on the external surface of the membrane, or whether it is capable of entering the hepatocyte as is the case for human fibroblasts. It is is suspected that 125I-EGF enters the cell, attempts will be made to determine the structural integrity of the molecule and whether it becomes associated with the nucleus or other sub-cellular organelles. We have shown that the cultured hepatocytes are capable of the biosynthesis and secretion of fibrinogen and transcobalamin II. We will use these serum proteins and albumin as marker proteins to examine the effects of EGF on the secretory processes in liver.